1. Technical Field
The present invention generally relates to biomedical devices, and especially ophthalmic lenses that are intended for direct placement on or in the eye such as contact lenses or intraocular lenses.
2. Description of Related Art
In the field of biomedical devices such as contact lenses, various factors must be considered in order to yield a material that has appropriate characteristics. For example, various physical and chemical properties such as oxygen permeability, wettability, material strength and stability are but a few of the factors that must be carefully balanced to provide a useable contact lens. Since the cornea receives its oxygen supply exclusively from contact with the atmosphere, good oxygen permeability is a critical characteristic for any contact lens material. Wettability is also important in that, if the lens is not sufficiently wettable, it does not remain lubricated and therefore cannot be worn comfortably in the eye. Accordingly, the optimum contact lens would have at least both excellent oxygen permeability and excellent tear fluid wettability.
For example, contact lenses made from silicone materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Hydrogels can absorb and retain water in an equilibrium state whereas non-hydrogels do not absorb appreciable amounts of water. Regardless of their water content, both hydrogel and non-hydrogel silicone contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
By introducing fluorine-containing groups into contact lens polymers, the oxygen permeability can be significantly increased. For example, U.S. Pat. No. 4,996,275 discloses using a mixture of comonomers including the fluorinated compound bis(1,1,1,3,3,3-hexafluoro-2-propyl)itaconate in combination with organosiloxane components. Fluorinating certain polysiloxane materials has been indicated to reduce the accumulation of deposits on contact lenses made from such materials. See, for example, U.S. Pat. Nos. 4,440,918; 4,954,587; 4,990,582; 5,010,141 and 5,079,319. However, fluorinated polymers can suffer from one or more of the following drawbacks: difficult and/or expensive synthetic routes, poor processability, low refractive index, poor wettability, poor optical clarity, poor miscibility with other monomers/reagents and toxicity.
Accordingly, it would be desirable to provide improved biomedical devices such as contact lenses that exhibit suitable physical and chemical properties, e.g., oxygen permeability and wettability, for prolonged contact with the body while also being biocompatible.